Innate Immunity is the most ancient and evolutionarily conserved central defense system that distinguishes host-self from non-self microbial pathogens in plants, animals and humans. It provides the first line of inducible defense against infectious diseases and underlies the prevention of constant and omnipresent microbial invasion. A key function of innate immunity is the detection of microbe-associated molecular patterns (MAMPs, such bacterial flagellin) by pattern recognition receptors and the launch of appropriate defense responses. Recent discoveries have revealed remarkable convergent evolution in the recognition of diverse MAMPs by leucine-rich-repeat receptors and the activation of multiple MAPK cascades in plants, animals and humans. Despite the universal and essential involvement of MAPK cascades in mediating MAMP signaling in plants, worms, flies, mammals and humans, the molecular mechanisms underlying the intertwined signaling webs remain mostly elusive due to the complexity of functional redundancy, mutant lethality and shared components in distinct signaling pathways. The goal of this research project is to establish a regulatory framework for the convergent MAMP signaling using Arabidopsis thaliana as a model system. The proposed experiments aim to integrate molecular, biochemical, cellular, genetic, and genomic approaches to dissect the multifunctional BAK1-MAPKKK complexes and MAPKK-MAPK cascades, and to analyze the downstream WRKY transcription factors in controlling diverse target genes in plant defense responses. Specifically, the project will focus on characterizing and integrating the functions of 15 Arabidopsis genes in flagellin signaling using cell- based assays, transgenic plants and loss-of-function mutants with specific defects in the flagellin receptor FLS2, receptor signaling partner BAK1, MAPKKK-MAPKK-MAPK cascades and WRKY transcription factors. Protein interaction, phosphorylation and ubiquitination assays, quantitative RT- PCR, whole-genome microarray and chromatin-immunoprecipitation will be carried out to elucidate the key and conserved signaling mechanisms in plant innate immunity. Three Specific Aims are: Aim 1. Analyze interactions and regulations of BAK1-MAPKKK signaling complexes Aim 2. Dissect the MAPKK-MAPK cascade functions in convergent MAMP signaling Aim 3. Define functions and regulations of WRKY transcription factors. PUBLIC HEALTH RELEVANCE: The powerful innate immune system underlies the prevention of constant and omnipresent microbial invasion, and provides the first line of inducible defense against infectious diseases in plants, animals and humans. A key function of innate immunity is the detection of microbe- associated molecular patterns (MAMPs) and the launch of appropriate defense responses. Recent discoveries have revealed remarkable convergent evolution in MAMP perception by leucine-rich- repeat pattern recognition receptors and the activation of multiple MAPK cascades. The proposed research from receptor kinase signaling complexes to intertwined MAPK cascades and WRKY transcriptional controls will discover novel and fundamental molecular mechanisms in innate immune signaling, and provide innovative tools for future improvement of agriculture, environment and renewable energy production, as well as human health in treating infectious, inflammatory and autoimmune diseases.